Seat base



FIG. 1 is a Right-Lateral view thereof;

FIG. 2 is a Frontal view thereof;

FIG. 3 is a Back view thereof;

FIG. 4 is a right elevation view thereof;

FIG. 5 is a left elevation view thereof;

FIG. 6 is a Top Elevation view thereof; and,

FIG. 7 is a Bottom Elevation view thereof.

The broken lines shown in the drawings depict environmental featuresthat form no part of the claimed design.

CLAIM The ornamental design for a seat base, as shown and described.